The Koopmans ionization potentials of XMe3 (X=N, P, As, Sb and Bi) have been calculated by using the relativistic effective core potentials ab initio method. The calculated band width, te relative intensity of bands and the relative position of shoulder peaks of the separated spectra are in agreement with those of the photoelectron spectra. The characteristics of the lone pair orbitals were discussed with orbital levels and orbital components. It is found that there is a good linear relation between some Mo levels of XMe3 and AO levels of the central atom X by linear regression analysis.

Key words: NITROGEN COMPOUNDS, BISMUTH COMPOUNDS, IONIZATION ENERGY, PHOSPHORUS COMPOUNDS, ANTIMONY COMPOUNDS, ARSENIC COMPOUNDS, ELECTRONIC ORBIT